Model simulations of the Bay of Fundy Gyre: 2. Hindcasts for 2005–2007 reveal interannual variability in retentiveness

Abstract

A persistent gyre at the mouth of the Bay of Fundy results from a combination of tidal rectification and buoyancy forcing (Aretxabaleta et al., J. Geophys. Res., vol. 113, 2008). Here we assess interannual variability in the strength of the gyre using data assimilative model simulations. Realistic hindcast representations of the Gyre are considered over the course of cruise surveys in 2005, 2006 and 2007. Assimilation of shipboard and moored ADCP velocities are used to improve the skill of the simulations, as quantified by comparison with non-assimilated drifter trajectories. Our hindcast suggest a weakening of the Gyre system during May 2005. Retention of simulated passive particles in the Gyre during that period was highly reduced. A recovery of the dense water pool in the deep part of the basin by June 2006 resulted in a return to particle retention characteristics similar to climatology. Retention estimates reached a maximum during May 2007 (sub-surface) and June–July 2007 (near-surface). Interannual variability in the strength of the gyre was primarily modulated by the stratification of the dense water pool inside the Grand Manan Basin. These changes in stratification may be attributed to mixing conditions the preceding fall/winter and/or advectively-driven modification of water mass properties.

Benthic nepheloid layers in the Gulf of Maine and Alexandrium cyst inventories

“…Based on these results, we suggest that southwesterly MCC transport of BOF cysts along the Maine coast provides an important contribution to the cyst inventories in the BNLs located to the southwest and downstream of the BOF. A similar northeast-to-southwest pattern has been observed and modeled in the propagation from the BOF to midcoast Maine of annual A. fundyense blooms via the MCC (Anderson et al, 2005; McGillicuddy et al, 2005). However, numerical model simulations of suspended cyst transport suggest the possibility of more modest advective length scales (Aretxabaleta et al 2014).…”

“…Of particular interest relative to these data is the existence of large, permanent sedimentary cyst beds in the BOF and off the central Maine coast/Penobscot Bay where cyst concentrations of ~10 5 −10 6 cysts m −2 within the upper 1 cm have been consistently reported from benthic surveys (Martin and Wildish, 1994; Anderson et al, 2005, 2014). These seedbeds have been proposed as the primary sources of the inoculum for the annual A. fundyense bloom in the gulf (Anderson et al, 2005; McGillicuddy et al, 2005; Anderson et al, 2014). …”

“…In the deep BNLs of Jordan and Wilkinson Basins that are inside the peripheries of the cyclonic gyres centered over the basins, mean tidal flows of 10–20 cm s- 1 dominate smaller residual (mean) flows (Pilskaln et al, 2013a). In the BOF where a massive A. fundyense seedbed exists, model simulations of the BOF cyclonic gyre reveal inter- and intra-annual variability in particle retention and advective interaction with the adjacent Gulf of Maine circulation (Aretxabaleta et al, 2008, 2009). Theoretically, it follows that such variability might also impact the resuspension and transport of cysts from the BOF seedbed into the gulf.…”

Understanding interannual, decadal level variability in paralytic shellfish poisoning toxicity in the Gulf of Maine: The HAB Index

“…Given the linkage between A. fundyense blooms in the BOF and those in eastern Maine (Aretxabaleta et al, 2008; 2009), and the linkages between blooms in western Maine and those in New Hampshire and Massachusetts Bay (Anderson, 1997), one wonders whether the patterns indicated by the Maine HAB Index are reflected in toxicity patterns in these upstream and downstream areas. Unfortunately, the data needed to calculate the HAB Index are not currently available for Massachusetts or the BOF, but other measures of toxicity can be examined in this context.…”

“…1; Anderson et al, 2005c; Anderson et al, this issue). Cysts germinate from the BOF seedbed, causing recurrent A. fundyense blooms within a retentive eddy at the mouth of the Bay that are self-seeding with respect to future outbreaks in that area (White and Lewis, 1982; Aretxabaleta et al, 2008, 2009; Martin et al, this issue). Some cells escape the retention zone and enter the eastern segment of the Maine Coastal Current (MCC) where they bloom.…”